Transmission properties of a novel optical waveguide structure based on Nafion polymer are investigated
by the technique of the m-line spectroscopy at a wavelength of 632.8nm. The refractive index profiles for
Nafion film for both TE and TM modes are found to be of quadratic nature with surface refractive indices
values of 1.3408 and 1.3446 respectively. The attenuation loss of this polymeric waveguide is found to be 1.53 dBcm-1
Devices based on optical technology for high speed communication networks require materials with large
nonlinear optical response in the ultrafast regime. Nonlinear optical materials have also attracted wide
attention as potential candidates for the protection of optical sensors and eyes while handling lasers. Optical
limiters have a constant transmittance at low input influence and a decrease in transmittance at higher
fluences and are based on a variety of mechanisms such as nonlinear refraction, nonlinear scattering,
multiphoton absorption and free carrier absorption. As we go from bulk to nanosized materials especially in
the strong quantum confinement regime where radius of the nanoparticle is less than the bulk exciton Bohr
radius, the optical nonlinearity is enhanced due to quantum confinement effect. This paper is on the
ultrafast nonresonant nonlinearity in free standing films of PbS quantum dots stabilized in a synthetic glue
matrix by a simple chemical route which provides flexibility of processing in a variety of physical forms.
Optical absorption spectrum shows significant blue shift from the bulk absorption onset indicating strong
quantum confinement. PbS quantumdots of mean size 3.3nm are characterized by X-ray diffraction and
transmission electron microscopy. The mechanism of nonlinear absorption giving rise to optical limiting is
probed using open z-scan technique with laser pulses of 150 fs pulse duration at 780 nm and the results are
presented in the nonresonant femtosecond regime. Irradiance dependence on nonlinear absorption are
discussed.
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